1. Field of the Invention
The present invention relates to visible light communication, and more particularly, to an apparatus and a method for aligning visible light communication devices by using a camera and a screen mounted to a mobile terminal.
2. Description of the Related Art
In general, visible light communication refers to a wireless communication technology using light in a visible wavelength range, and in recent years, studies on the visible light communication have been increasingly conducted along with proliferation of a light emitting diode (LED). Recently, the visible light communication mainly using the LED as a light source for communication has been more spotlighted due to lack of frequencies in a radio frequency (RF) band, a possibility of cross talk between various wireless communication technologies, and an increased demand for communication security.
In the general visible light communication, a transmitter emits visible light by using the LED or a laser diode (LD) as the light source, and a receiver processes the visible light by using a photo diode (PD). As light emission efficiency of the LED is improved and a price of the LED is lowered, the LED is becoming more common in a market of general lighting such as fluorescent lamps and in a market of special lighting employed in portable devices, displays, vehicles, traffic signals, and advertising boards.
Infrared-ray communication may be given as an example of technology with a similar characteristic to the visible light communication. FIG. 1 is a flowchart showing a conventional process of performing data transmission by using infrared-ray.
Referring to FIG. 1, a wireless communication process using the infrared-ray includes an infrared-ray communication activation step 101, an external infrared-ray communication device discovery step 102, a communication method determination step 103, a connection step 104, a data transmission step 105, a disconnection determination step 106, and a communication deactivation step 107. A user approximately orients the infrared-ray communication device to align communication links through such a series of steps as described above.
A data transmission method between a transmission side and a reception side which perform the infrared-ray communication will be described hereinafter. FIG. 2 is a signal flow diagram showing an example of a data transmission method using the existing infrared-ray.
Referring to FIG. 2, if a transmission side 201 transmits data to a reception side 202 in step 203, the reception side 202 transmits an acknowledge (ACK) signal for acknowledging the receipt of the received data to the transmission side 201 in step 204. In this way, the data transmission is performed between the transmission side 201 and the reception side 202.
The above-described method using the infrared-ray may be similar to a method using the visible light in that they use the LED, except for the difference in the band in which the light source is used. In other words, it can be said that the biggest difference between the infrared-ray communication and the visible light communication is visibility, and in this regard, the visible light communication which is currently being developed has a distinctive feature as compared with the infrared-ray communication. That is, the biggest feature of the visible light communication in comparison with the infrared-ray communication is that the visible light communication uses a light source in a visible light band, which enables the user to directly identify the link situation of communication.
A frame, referred to as a visibility frame, which is not real data and is arranged to be shown to the user, may be intentionally transmitted to maximize an advantage of the visibility. The visibility frame may be used for informing of states of peripheral device discovery, connection, and data transmission in a process occurring when the communication is performed, or for orienting one communication device toward a counterpart device in order to align the communication devices with each other before the communication between the communication devices. In this event, due to straightness of the light source used in the visible light communication, it is of great importance to align the communication devices with each other during the communication between the communication devices.
That is, as in the visible light communication, in a case where the straightness of a communication medium is strong and a line of sight (LOS) is important, the alignment between the communication devices is significantly important. Further, when the user desires to align the communication links, the visibility may help the user a lot.
However, as the distance between two devices attempting to communicate with each other increases, the visibility is deteriorated. This problem may be solved if the brightness of the light source is increased by increasing the power of a transmitted signal. However, such a power increase naturally causes incidental increase of power consumption. Further, an increase in the power of the signal may cause the devices themselves to generate heat. Moreover, the brightness of the light source may be increased so much that the light source may act as an obstruction to other peripheral devices or the user.